Initial support for Libre Computer Amlogic Boards

This MR adds support for two Amlogic SBCs from Libre Computer; AML-S905X-CC (aka. lepotato) and AML-S805X-AC (aka. lafrite).

This MR supplies its own U-Boot for lafrite, which boots from SPI by default. To make use of this U-Boot instead of the one on the SPI you need to wipe it:

# flashrom -p linux_mtd -E # erase SPI flash

Wiki pages:

• AML-S905X-CC-V1.0: https://wiki.postmarketos.org/wiki/Libre_Computer_AML-S905X-CC-V1.0_(librecomputer-lepotato)
• AML-S805X-AC-V1.0: https://wiki.postmarketos.org/wiki/Libre_Computer_AML-S805X-AC-V1.0_(librecomputer-lafrite)

Cc: @exkc